Mold device

ABSTRACT

A mold device is capable of producing a member formed from aluminum, and includes a mold and a molten metal supply part. The mold is capable of forming a cavity into which molten aluminum is charged. The mold has a base part formed from iron and a surface layer part. The surface layer part is provided on the cavity side of the base part and contains 20 weight % or more of chromium. A dichromium trioxide film is formable on a surface of the cavity side of the surface layer part. The molten metal supply part is capable of supplying molten aluminum into the cavity.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of International Application No. PCT/JP2019/005799 filed on Feb. 18, 2019, which is based on and claims the benefit of priority from Japanese Patent Application No. 2018-34626 filed on Feb. 28, 2018. The contents of these applications are incorporated herein by reference in their entirety.

BACKGROUND

The present invention relates to a mold device.

There have been conventionally known mold devices used for a die-casting method by which a molten metal in a mold is pressurized to produce a member in a desired shape.

SUMMARY

The present disclosure is a mold device that is capable of producing an aluminum die-cast member and includes a mold and a molten metal supply part.

The mold is capable of forming a cavity into which molten aluminum is charged. The mold has a base part formed from iron and a surface layer part that is provided on the cavity side of the base part, contains 20 weight % or more of chromium, and is capable of forming a dichromium trioxide film on a surface of the cavity side.

The molten metal supply part is capable of supplying molten aluminum into the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the present disclosure will be more clarified by the following detailed descriptions with reference to the accompanying drawings. The drawings are as follows:

FIG. 1 is a schematic view of a mold device according to a first embodiment;

FIG. 2 is an enlarged view of a part II shown in FIG. 1;

FIG. 3 is a schematic diagram describing operations of the mold device according to the first embodiment;

FIG. 4 is a schematic diagram describing operations of the mold device according to the first embodiment, which shows the next state to that shown in FIG. 3;

FIG. 5 is a schematic diagram describing operations of the mold device according to the first embodiment, which shows the next state to that shown in FIG. 4;

FIG. 6 is a photograph showing results of experiment on the mold device according to the first embodiment;

FIG. 7 is a photograph showing results of experiment on a mold device according to a comparative example;

FIG. 8 is a schematic view of a mold device according to a second embodiment; and

FIG. 9 is a schematic diagram describing operations of the mold device according to the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There have been conventionally known mold devices used for a die-casting method by which a molten metal in a mold is pressurized to produce a member in a desired shape. For example, JP 2007-118035 A describes a mold device in which the surface of a mold to contact molten metal is coated with a mold release agent containing an organic acid or organic acid salt having a reducing property with a concentration of 0.01 weight % or more at the point of use that is equal to or less than a predetermined concentration which is the stability limit of a mold release emulsion in undiluted form.

To mold a member from aluminum, molten aluminum is charged into a mold cavity. In mold devices into which molten aluminum is to be charged, the surface of a mold cavity is subjected to nitriding treatment or multi-layer coating with heat-resistant ceramics as measures against adhesion of aluminum to the mold and dissolution loss. In the process of the nitriding treatment, however, a nitrogen diffusion layer is gradually thermally decomposed by contact with the high-temperature molten aluminum, thereby causing a lack of durability. In the case of the multi-layer coating with heat-resistance ceramics, if the molten aluminum intrudes into the coating from a film defect, the base part of the coated mold erodes by reaction with the molten aluminum, whereby the heat-resistant ceramic layers may peel off. The present disclosure has been devised considering the foregoing problems. An object of the present disclosure is to provide a mold device that prevents adhesion with molten aluminum and mold damage.

The present disclosure is a mold device that is capable of producing an aluminum die-cast member and includes a mold and a molten metal supply part.

The mold is capable of forming a cavity into which molten aluminum is charged. The mold has a base part formed from iron and a surface layer part that is provided on the cavity side of the base part, contains 20 weight % or more of chromium, and is capable of forming a dichromium trioxide film on a surface of the cavity side.

The molten metal supply part is capable of supplying molten aluminum into the cavity.

In the mold device of the present disclosure, the surface layer part with the cavity side of the base part of the mold contains 20 weight % or more of chromium. This makes it possible to form a dichromium trioxide film that is a dense passive film relative to the molten aluminum and has a non-wetting property and anti-corrosion property against the molten aluminum, on the surface of the cavity side of the surface layer part. Accordingly, when the molten aluminum is charged into the cavity, it is possible to reliably prevent adhesion between the base part of the mold and the molten aluminum.

The dichromium trioxide film may peel off from the surface layer part due to the cooling/heating cycle of the mold, sliding of the aluminum die-cast member when being removed from the mold, or the like. In the mold device of the present disclosure, even if the dichromium oxide film peels off from the mold, the chromium migrates to the surface of the surface layer part in the mold to form a new dichromium trioxide film. This prevents adhesion between the base part of the mold and the molten aluminum for a relatively long period of time, thereby preventing breakage of the mold and lengthening the lifetime of the mold device.

Hereinafter, a plurality of embodiments will be described with reference to the drawings. In the description of the plurality of embodiments, significantly identical parts are denoted with identical reference signs and redundant description thereof is omitted.

First Embodiment

A mold device 1 according to a first embodiment will be described with reference to FIGS. 1 to 6. The mold device 1 is used for die-casting a member 5 (see FIG. 5) as an aluminum die-cast member□molded out of aluminum. The mold device 1 includes a mold 10 and a molten metal supply part 20 as shown in FIG. 1.

The mold 10 has a movable mold 11 and a fixed mold 12. In the mold 10, the movable mold 11 and the fixed mold 12 form a cavity 100 into which molten aluminum is chargeable.

The movable mold 11 is formed from a metal, for example, steel. The movable mold 11 is movable relative to the fixed mold 12 as shown by an open arrow F0. The movable mold 11 has a first space 110 that is open on the fixed mold 12 side as shown in FIG. 1. The first space 110 constitutes part of the cavity 100. FIG. 2 is an enlarged view of a surface of the movable mold 11 to contact the molten aluminum. The movable mold 11 has a base part 111, a concentration transition part 112, and a surface layer part 113. In the present embodiment, the base part 111, the concentration transition part 112, and the surface layer part 113 are integrally formed.

The base part 111 is a part that constitutes a basic structure of the movable mold 11. The base part 111 is relatively separated from the first space 110 as shown in FIG. 2. In the present embodiment, the base part 111 is formed from iron with a carbon concentration of 0.07 weight % or less.

The concentration transition part 112 is a part that is provided on the first space 110 side of the base part 111. The concentration transition part 112 is formed such that the chromium concentration constantly increases from the base part 111 toward the surface layer part 113 described later. FIG. 2 shows the boundary between the base part 111 and the concentration transition part 112 by a virtual line VL111.

The surface layer part 113 is a part that is provided on the first space 110 side of the concentration transition part 112 and constitutes an inner wall for forming the first space 110. The surface layer part 113 is formed with a thickness of 30 μm or more and 200 μm or less. The surface layer part 113 is formed with a chromium concentration of 20 weight % or more by a chromizing process such as a gas-phase method or powder method, or a thermal diffusion process on a chromium-coated article, for example. This forms a dichromium trioxide (hereinafter, abbreviated as (Cr₂O₃) film 114 on the first space 110 side of the surface layer part 113 (see FIG. 3). The Cr₂O₃ film 114 has a heat-proof temperature of 1350 degrees that is higher than an aluminum pouring temperature of 680 degrees, and is characteristically flawless. In the present embodiment, the Cr₂O₃ film 114 is formed with a thickness of 3 nm or more, for example. FIGS. 3 to 5 each show the mold device with differences in scale such that the formation of the Cr₂O₃ film 114 is easy to see. FIG. 2 shows the boundary between the concentration transition part 112 and the surface layer part 113 by a virtual line VL 112, and FIG. 3 shows the boundary between the Cr₂O₃ film 114 and another part in the surface layer part 113 by a virtual line VL1 13.

The fixed mold 12 is formed from a metal, for example, steel. The fixed mold 12 is fixed in an immobile manner and has a second space 120 that is open on the movable mold 11 side and a communication hole 121 as shown in FIG. 2. The second space 120 constitutes part of the cavity 100. That is, the cavity 100 is formed from the first space 110 and the second space 120. The communication hole 121 communicates the second space 120 to the outside of the fixed mold 12.

The fixed mold 12 is structured in the same manner as the movable mold 11 and has a base part, a concentration transition part, and a surface layer part. The base part, concentration transition part, and surface layer part of the fixed mold 12 respectively have the same features of the base part 111, the concentration transition part 112, and the surface layer part 113 of the movable mold 11. The base part, concentration transition part, and surface layer part of the fixed mold 12 are integrally formed.

The molten metal supply part 20 is formed to be capable of supplying molten aluminum to the cavity 100 in the mold 10. The molten metal supply part 20 supplies the molten aluminum to the second space 120 via the communication hole 121 in the fixed mold 12.

Next, operations of the mold device 1 will be described. FIGS. 3 to 5 show changes in the enlarged views of the surface layer part 113 and its neighborhood of the movable mold 11 subjected to a die-casting method using the mold device 1. Hereinafter, the operations of the movable mold 11 will be described for the sake of convenience, but the following description is also applied to the fixed mold 12.

Before charging of the molten aluminum into the cavity 100, the mold device 1 has the Cr₂O₃ film 114 formed on the surface of the surface layer part 113 of the movable mold 11 and the surface layer part of the fixed mold 12 as shown in FIG. 3.

First, the movable mold 11 and the fixed mold 12 are combined to form the cavity 100. Molten aluminum 4 is supplied from the molten metal supply part 20 into the mold 10 with the cavity 100. The molten aluminum 4 supplied from the molten metal supply part 20 is pressed and charged into the cavity 100. The molten aluminum 4 pressed into the cavity 100 spreads onto a surface 115 of the Cr₂O₃ film 114 opposite to the concentration transition part 112 as shown in FIG. 4. That is, the movable mold 11 and the fixed mold 12 are brought into contact with the molten aluminum via the Cr₂O₃ film 114.

The molten aluminum 4 charged in the cavity 100 becomes solidified to mold the member 5. When the member 5 is molded, the movable mold 11 is moved and separated from the fixed mold 12, and the member 5 is taken out of the mold 10. At this time, the Cr₂O₃ film 114 is peeled and dropped off from the surface layer part 113 of the movable mold 11 and the surface layer part of the fixed mold 12 by the movement of the member 5 as shown by an open arrow F1 in FIG. 5.

After the member 5 is taken out of the mold 10, the Cr₂O₃ film 114 is reproduced on the surface of the surface layer part 113 as shown in FIG. 3. The molten aluminum pressed into the cavity 100 for next production of the member 5 spreads over the surface 115 of the reproduced Cr₂O₃ film 114.

Description will be given as to a change occurring on the surface of a mold on the cavity side after the removal of a member molded by pressing molten aluminum into a cavity with reference to FIGS. 6 and 7. The photographs in FIGS. 6 and 7 both show cross-sections of the surface of the mold on the cavity side after the removal of the molded member from the cavity.

FIG. 6 is the photograph of the cross section and its neighborhood of the surface of the mold 10 on the cavity 100 side in die-casting using the mold device 1. In the mold device 1 of which the photograph of the cross section is shown in FIG. 6, the surface of the mold 10 on the cavity 100 side has undergone chromizing treatment.

FIG. 7 is the photograph of the cross section and its neighborhood of the surface of the mold on the cavity side in die-casting using a mold device as a comparative example having no components equivalent to the surface layer part and the concentration transition part of the mold device 1 (hereinafter, called mold device in the comparative example). In the mold device in the comparative example of which the photograph of the cross section is shown in FIG. 7, the surface of the mold on the cavity side has undergone nitriding treatment.

It is seen from the photograph of the surface and its neighborhood of the mold device in the comparative example shown in FIG. 7 that the entire surface of the mold (the part shown by a solid-line arrow A7 in FIG. 7) is eroded to have projections and recesses. On the other hand, it is seen from the photograph of the surface and its neighborhood of the mold device 1 shown in FIG. 6 that the surface is not eroded but is comparatively flat (the part shown by a solid-line arrow A6 in FIG. 6). In addition, the surface shown in FIG. 6 is not likely to suffer pitting corrosion from the molten aluminum.

In the mold device 1 according to the first embodiment, the surface layer part 113 provided on the base part 111 of the mold 10 on the cavity 100 side contains 20 weight % or more of chromium. This makes it possible to form a Cr₂O₃ film that is a dense passive film relative to the molten aluminum 4 and has a non-wetting property and anti-corrosion property against the molten aluminum 4, on the cavity 100 side of the surface layer part 113. Accordingly, the mold device 1 can reliably prevent the adhesion between the base part 111 of the mold 10 and the molten aluminum 4.

In the mold device 1 according to the first embodiment, the surface of the surface layer part of the mold 10 is kept relatively flat as shown in FIG. 6. This improves the dimensional accuracy of the molded member 5 while maintaining the outer appearance quality of the member 5.

In the mold device 1 according to the first embodiment, when the member 5 molded in the cavity 100 is taken out of the mold 10, the Cr₂O₃ film 114 may peeled off from the surface layer part 113. In the mold device 1 according to the first embodiment, however, the chromium in the mold 10 migrates to the surface of the surface layer part 113 to form the new Cr₂O₃ film 114. Thus, the mold device 1 according to the first embodiment can prevent the adhesion between the mold 10 and the molten aluminum 4 for a relatively long time. This makes it possible to prevent the breakage of the mold 10 and lengthen the lifetime of the mold device 1. Since the adhesion between the mold 10 and the molten aluminum 4 can be prevented for a relatively long time, it is possible to reduce the number of man-hours for maintenance of the mold 10.

In the mold device 1 according to the first embodiment, the concentration transition part 112 is formed such that the chromium concentration constantly increases from the base part 111 toward the surface layer part 113. Accordingly, in the first embodiment, it is possible to prevent the Cr₂O₃ film 114 from easily peeling off from the mold 10 due to heat stress.

In the mold device 1 according to the first embodiment, the surface layer part 113 is formed with a thickness of 30 μm or more and 200 μm or less. This is because the Cr₂O₃ film 114 is unlikely to be reproduced when the thickness of the surface layer part 113 is smaller than 30 μm, whereas the surface layer part 113 becomes hard and the Cr₂O₃ film 114 is likely to peel off from the surface layer part 113 when the thickness of the surface layer part 113 is larger than 200 μm. Therefore, in the first embodiment, setting the thickness of the surface layer part 113 to 30 μm or more and 200 μm or less makes it possible to keep the Cr₂O₃ film 114 in an appropriate state.

In the mold device 1 according to the first embodiment, the base part of the movable mold 11 and the fixed mold 12 have a carbon concentration of 0.07 weight % or less. This prevents the chromium contained in the concentration transition parts on the cavity 100 side of the base part from being trapped by carbon of the base part. Therefore, in the first embodiment, it is possible to keep the chromium concentration in the concentration transition part and the surface layer part at desired values.

Second Embodiment

Next, a mold device according to a second embodiment will be described with reference to FIGS. 8 and 9. The second embodiment is different from the first embodiment in including an oxidant supply part.

A mold device 2 according to the second embodiment of the present disclosure will be described with reference to FIGS. 8 and 9. The mold device 2 includes a mold 10, a molten metal supply part 20, and an oxidant supply part 30. The oxidant supply part 30 has an oxidant tank 31 and an injection nozzle 32.

The oxidant tank 31 is provided outside the mold 10. The oxidant tank 31 stores an oxidizing acid that reacts with the chromium content of the mold 10 to generate Cr₂O₃, such as nitric acid, sulfuric acid, or organic acid such as acetic acid.

The injection nozzle 32 connects to the oxidant tank 31 via a pipe 33. The injection nozzle 32 is movable relative to the mold 10. The injection nozzle 32 is movable to be positioned between the movable mold 11 and the fixed mold 12 that are separated from each other as shown in FIG. 9. The injection nozzle 32 has a plurality of injection pipes 321. The injection pipes 321 can inject an oxidant from the oxidant tank 31 onto a surface 115 of a surface layer part 113 of the movable mold 11 and a surface 125 of a surface layer part of the fixed mold 12 on the second space 120 side.

In the process of molding a member 5 in the mold device 2, before the Cr₂O₃ film 114 is apparently about to drop off, the injection nozzle 32 is inserted into between the movable mold 11 and the fixed mold 12 that are separated from each other as shown in FIG. 9. The inserted injection nozzle 32 injects the oxidant from the plurality of injection pipes 321 onto the surfaces of the movable mold 11 and the fixed mold 12 on the cavity 100 side (as shown by two-dot chain lines 139 in FIG. 9). After that, the mold 10 and the oxidant are heated by the molten aluminum so that the Cr₂O₃ film 114 is generated on the respective surfaces 115 and 125 of the movable mold 11 and the fixed mold 12 on the cavity 100 side.

In the mold device 2 according to the second embodiment, in the process of molding the member 5, the oxidant is supplied onto the surfaces 115 and 125 of the movable mold 11 and the fixed mold 12 on the cavity 100 side in accordance with the states of the surfaces 115 and 125, thereby to generate the Cr₂O₃ film 114 in a positive manner. Accordingly, reproducing the Cr₂O₃ film 114 or reinforcing the already generated Cr₂O₃ film 114 reliably prevents the adhesion between the base part 111 of the mold 10 and molten aluminum 4. Therefore, according to the second embodiment, it is possible to not only produce the advantageous effects of the first embodiment but also further lengthen the lifetime of the mold device 1.

Other Embodiments

In the foregoing embodiments, the mold has the concentration transition part between the base part and the surface layer part. However, the concentration transition part may not be provided.

In the foregoing embodiments, the base part, the concentration transition part, and the surface layer part are integrally formed. However, these parts may not be integrally formed. For example, a high-concentration chromium material may be attached to the surface layer of the base part to enhance adhesiveness by heat diffusion or the like. In this case, the base part may be a member with a relatively high carbon concentration.

In the foregoing embodiments, the concentration transition part is formed such that the chromium concentration constantly increases from the base part toward the surface layer part. However, the change in the chromium concentration of the concentration inclination part is not limited to this. The concentration transition part may be merely formed such that the chromium concentration continuously changes between the surface layer part with a chromium concentration of 20 weight % or more and the base part with a relatively low chromium concentration.

In the foregoing embodiments, the surface layer part has a thickness of 30 μm or more and 200 μm or less. However, the thickness of the surface layer part is not limited to this range.

In the foregoing embodiments, the base part has a carbon concentration of 0.07 weight % or less. However, the carbon concentration of the base part is not limited to this. The portion of the base part on the concentration transition layer side may be decarbonized so that only this portion has a carbon concentration of 0.07 weight % or less. Otherwise, the base part may be processed such that the surface of steel with a carbon concentration of about 0.4 weight % on the space side is chromium-plated and heated to form a Cr₂O₃ film on the surface of the chromium layer that is penetrated and adhered to the interface of the base part of the mold. The Cr₂O₃ film can prevent the adhesion between the base part of the mold and the molten aluminum for a relatively long time.

In the second embodiment, the oxidant is injected from the injection pipes. However, the method for supplying the oxidant onto the surface of the mold on the cavity side is not limited to this. For example, the oxidant may be applied to the surface of the mold on the cavity side.

The present disclosure described so far is not limited to these embodiments but can be carried out in various manners without deviating from the scope of the present disclosure.

The present disclosure has been described so far according to the embodiments, but it is noted that the present disclosure is not limited to the foregoing embodiments or structures. The present disclosure includes various modifications and changes in a scope of equivalent. In addition, various combinations and modes, and other combinations and modes including only one element of the foregoing combinations and modes, less or more than the one element are included in the scope and conceptual range of the present disclosure. 

What is claimed is:
 1. A mold device that is capable of producing an aluminum die-cast member, comprising: a mold capable of forming a cavity into which molten aluminum is charged and has a base part formed from iron and a surface layer part, the surface layer part being provided on the cavity side of the base part, containing 20 weight % or more of chromium, and being capable of forming a dichromium trioxide film on a surface of the cavity side; and a molten metal supply part capable of supplying molten aluminum into the cavity, wherein the mold has a concentration transition part that is provided between the base part and the surface layer part and in which a chromium concentration constantly increases from the base part toward the surface layer part, and the base part, the concentration transition part, and the surface layer part are integrally formed.
 2. A mold device that is capable of producing an aluminum die-cast member, comprising: a mold capable of forming a cavity into which molten aluminum is charged and has a base part formed from iron and a surface layer part, the surface layer part being provided on the cavity side of the base part, containing 20 weight % or more of chromium, and being capable of forming a dichromium trioxide film on a surface of the cavity side; a molten metal supply part capable of supplying molten aluminum into the cavity, and an oxidant supply part capable of supplying an oxidant onto the surface of the surface layer part on the cavity side.
 3. The mold device according to claim 2, wherein the oxidant is an oxidizing acid.
 4. The mold device according to claim 1, wherein the surface layer part has a thickness of 30 μm or more and 200 μm or less.
 5. The mold device according to claim 1, wherein the base part has a carbon concentration of 0.07 weight % or less. 